1. Field of the Invention
Implementations of various technologies described herein generally relate to seismic data processing. In particular, various technologies described herein relate to a method for estimating properties of a subsurface area of the earth, such as anisotropic parameters.
2. Description of the Related Art
For many years, seismic exploration for oil and gas has been conducted by use of a source of seismic energy and the reception of the energy generated by the source by an array of seismic detectors. On land, the source of seismic energy may be a high explosive charge or another energy source having the capacity to deliver a series of impacts or mechanical vibrations to the earth's surface. Acoustic waves generated by these sources travel downwardly into geological formations in the earth's subsurface and are reflected back from strata boundaries and reach the surface of the earth at varying intervals of time, depending on the distance traveled and the characteristics of the subsurface traversed. These returning waves are detected by the sensors, which function to transform such acoustic waves into electrical signals that represent features of geological formations. The detected signals are recorded for processing using digital computers. The processing then generates seismic data which can be analyzed to determine the presence or absence of probable locations of hydrocarbon deposits.
Typically, an array of sensors is laid out along a line to form a series of detection locations. More recently, seismic surveys are conducted with sensors and sources laid out in generally rectangular grids covering an area of interest, rather than along a single line, to enable construction of three dimensional views of reflector positions over wide areas. Normally, signals from sensors located at varying distances from the source are added together during processing to produce “stacked” seismic traces. In marine seismic surveys, the source of seismic energy is typically air guns. Marine seismic surveys typically employ a plurality of sources and/or a plurality of streamer cables, in which seismic sensors are mounted, to gather three dimensional seismic data.
When determining the presence or absence of probable locations of hydrocarbon deposits, estimates of anisotropic parameters or stresses on the earth subsurface may be very useful. The importance of anisotropic stress estimates increases when anisotropic stresses are not equal to each other and when some preferred directions, e.g., directions of maximum and minimum anisotropic stresses, exist in geological media.
Examples of applications requiring good knowledge of existing anisotropic stresses include planning of drilling operation and mine construction. In those situations, poor estimates of anisotropic stresses may lead to additional costs and safety problems related to geological hazards and instability of a borehole or a mine. Furthermore, the development of many existing oil fields and orientation of fractures are typically controlled by direction of maximum horizontal anisotropic stresses. Therefore, anisotropic stress characterization performed prior to production may reduce risk in reservoir management decisions, particularly for production in areas having salt bodies.